This invention relates to ceramic pouring filters for use with molten metal, for instance, in the casting of molten metals, such as nickel base high temperature alloys used in casting of turbine blade elements, iron, aluminum or stainless steel. It is customary to pass the molten metal through a pouring filter before it enters the mold cavity.
The commercially available filters for such uses are of various types. Cellular ceramic filters, which have a honeycomb type of construction made up relatively deep cells of square cross-section, are described in the article by Day in Modern Casting, April, 1984, pages 16-18. Among the other types of commercial filters are ball filters, bonded particles, bonded or fused foam filters and fibrous filters. A ball filter is essentially a relatively deep box filled with balls, usually of about 3/4 inch diameter, of alumina or similar ceramic material. A bonded particle filter is made by bonding together grains of a ceramic material, which may be fabricated from crystalline aluminum oxide or silicon carbide for instance. One type of foam filter is a porous foam of phosphate-bonded alumina or zircon. A foam filter may be prepared by a method which involves impregnating an organic foam (such as polyurethane foam) with a dispersion of ceramic ingredients, followed by firing, during which the organic foam is burned away. Fibrous filters may be of woven fiberglass or of non-woven ceramic fibers.
In accordance with one aspect of this invention a pouring filter, for use in the casting of molten metals, comprises a plurality of multiply apertured ceramic elements, which are closely spaced, with their apertures in staggered relationship. The filter is strong, economical to manufacture, readily inspectable to insure against hidden internal defects present in other filters, and provides controlled removal of fine particles of undesired impurities at good flow rates.